Stressed or Healthy Pregnant Migrants?

Ilka Steiner, University of Geneva, nccr - on the move

Results regarding the “healthy migrant” effect in birth outcomes are somewhat inconclusive regarding migrants living in developed countries. While several studies have found as good or better birth outcomes of the foreign-born compared to the native-born, other studies report the contrary. According to the “acculturation paradox”, the length of exposure to the host country can be positively correlated with adverse birth outcomes, inter alia due to more stressful living situations in the host country.

Nevertheless, there are no studies investigating the impact of stress induced by international migration itself. Thus, we propose to compare mothers of different migratory status’ giving birth in Switzerland between 2010 and 2014 and to test for their birth outcome, that is low birth weight and preterm births. The analyses are based on Swiss longitudinal register data and on logistic regression analyses. Switzerland presents an interesting case to study. In 2014, a high 6,7% of all infants born were of low birth weight; a situation that is somewhat due to the large foreign-born population residing in Switzerland.

First results indicate a healthy migrant effect for migrants that arrived during the third trimester of pregnancy. Stress only seems to result in low birth weight (and not in preterm delivery) when migrating during the first and second semester of pregnancy. Finally, the “acculturation paradox” also seems to apply to the Swiss context, where pre-pregnancy migrants with a duration of residence of at least ten years present the highest risk of adverse birth outcomes.


Introduction

Due to an increase in immigration flows to developed countries, the number of foreign-born women in childbearing age is growing. The literature on birth outcomes of this specific population frequently evokes either the “healthy migrant” effect, referring to the association between the foreign-born status and birth outcomes and/or the “epidemiological paradox”, referring to the impact of low socioeconomic status on favorable birth outcomes among foreign-born women. Results regarding the “healthy migrant” effect in birth outcomes are however somewhat inconclusive regarding migrants living in developed countries. While several studies have found as good or better birth outcomes of the foreign-born compared to the native-born, other studies report the contrary.

It seems that time since immigration, and thus exposure to the host country, plays an important role. In fact, the longer migrants stay, the higher is the risk of preterm birth. This finding is also referred to as the “acculturation paradox”. The literature has shown that stressful life events during pregnancy have an impact on birth outcomes.

Nevertheless, there are no studies investigating the impact of stress induced by international migration itself. Thus, we propose to compare birth outcomes (low birth weight and preterm births) of mothers of different migratory status’ giving birth in Switzerland between 2010 and 2014. Switzerland presents an interesting case, because in 2014, 6,7% of all infants born were of low birth weight. Despite its high standard of living, this value is just situated beneath the Eurozone or OECD averages. This situation is somewhat due to the large foreign-born population residing in Switzerland.

Data

We use a Swiss longitudinal database, that is based on several Swiss registers. We consider live births from the civil register that occurred between January 1, 2010 and December 31, 2014. Only singleton births were included. In total, our data set contains 389,282 observations.

Research methods

Besides descriptive statistics, we apply logistic regression analyses. We consider two different outcomes, both widely used in the literature: low birth weight, that is if the child was born with less than 2500g., and preterm birth, that is if the child was born after less than 37 weeks of gestation.

Moreover, we distinguish between three broad population groups to retrace the varying degrees of exposure to the Swiss context. First, we separate the Swiss-born individuals (SB). Second, pre-pregnancy migrants (PPM) was subdivided according to the length of stay before pregnancy in Switzerland: PPM-C arrived during their childhood (before ten years of age), PPM-L (long) have more than ten years of residence, PPM-SM (short and medium) are immigrants with zero to ten years of duration of residence. The latter serve as the control group. Third, PM (pregnant migrants) are foreign-born individuals that arrived during the first (PM-1), the second trimester (PM-2) and the third trimester (PM-3).

We include six covariates in our analyses. First, mother’s age at delivery was included as dichotomous variable, under 35 years old and 35 and over. Second, civil status distinguishes singles, married and divorced/widowed individuals. Third, the mothers’ nationalities were regrouped according to the Human Development Index of 2016 (HDI) into very high HDI (>0.8), high HDI (>0.7 and <0.8), medium and low HDI (<0.7). Fourth, if available, we calculate the monthly average of both parent’s salary nine months before and three months after birth. Finally, we control for the gender of the child and the child’s parity (1st, 2nd, 3rd+ child of the same mother).

First results and expected findings

For all the covariates that we consider, two subpopulations stand out. While PPM-L present a general socio-demographic profile that is more at risk of adverse birth outcomes all PM categories seem to be at lower risk.

Regarding birth outcomes, 4.5% of all babies born in our sample were of low birth weight and 5.4% were born preterm. The values for SB and PPM-C are very similar to the average observed in the sample. While PPM-L present worse outcomes than the average (respectively 5% for low birth weight and 6.3% for preterm), PPM-SM present better birth outcomes (4.2% and 5.1%). Finally, PM present better outcomes regarding preterm births compared to the average, with a much lower share for third trimester migrants (4.1%). The results for the birth weight are more diverse. While PM-1 are on average, PM-2 have a higher share and PM-3 a much lower share.

First results of the logistic regression seem to support these descriptive finding, indicating a healthy migrant effect for migrants that arrived during the third trimester of pregnancy. Stress only seems to result in low birth weight (and not in preterm delivery) when women migrate during the first and second semester of pregnancy. Finally, the “acculturation paradox” also applies to the Swiss context, where pre-pregnancy migrants with a duration of residence of at least ten years present the highest risk of adverse birth outcomes.

Presented in Session 1163: Health, Wellbeing, and Morbidity